In recent years, digital mobile multimedia broadcast technologies and standards have developed rapidly, and various standards provide an end user of mobile multimedia broadcast with many service contents, for example, programs such as advertisings, weather forecasts, news, sport programs, variety shows, multimedia broadcast plays and movies. The users can choose the mobile multimedia broadcast service programs according to their own preferences.
A conditional access system (CAS) is a system for controlling the receiving of broadcast services or programs by subscribers, that is, the subscribers can only watch the entitled broadcast services or programs. The CAS is the key to achieve personalized services, and the basic purpose is to perform entitlement control and entitlement management of users in a television system, so as to realize paid services of a digital broadcast system.
The china mobile multimedia broadcasting (CMMB) system sends multimedia broadcast services in a time division multiplexing mode. The duration of a broadcast channel frame is 1 second, which is composed of 40 time slots of 25 milliseconds. One or more time slots may transmit data encapsulated in one multiplexing frame. In the multiplexing frame structure of the mobile multimedia broadcast, a multiplexing frame is divided into three parts which are a multiplexing frame header, a multiplexing frame payload and a multiplexing frame filling, as shown in FIG. 1. A mode in which control message and business data are separated is adopted for transmitting in the mobile multimedia broadcast technology. A zero multiplexing frame (MF_ID=0) is correspondingly used for encapsulating the control message when the time slot is used as a control channel, and a non-zero multiplexing frame (MF_ID!=0) is correspondingly used for encapsulating service data when the time slot is used as a data channel. For the service multiplexing frame payload, it can be divided into one or more multiplexing sub-frames, a video segment, an audio segment and a data segment are encapsulated after a sub-frame header in each sub-frame, as shown in FIG. 2.
In the front end of the CA system, a control word (CW) is encrypted into an entitlement control message (ECM) and encapsulated in a data segment of a multiplexing sub-frame; a service key (SK) is encrypted into an entitlement management message (EMM) which independently occupies one multiplexing sub-frame, and is sent to the air through channel modulation performed by a modulator. As shown in FIG. 3, the basic procedure for processing data of a terminal CA module is as follows: a multiplexing frame is obtained by signal tuning of a tuner, and an ECM, an EMM and an electronic service guide (ESG) in the multiplexing sub-frame are obtained by demultiplexing of a demultiplexer respectively; then a session description protocol (SDP) is obtained through extracting the ESG by an ESG module, and a CA database performs decryption operations using the ECM, the EMM and the SDP; finally, a control word (CW) is generated, a descrambling module descrambles the scrambled audio and video data after obtaining the CW, and clear stream data of audio and video is obtained and sent to a player to be played directly.
In the multimedia broadcast technology, a general method for updating a CA plug-in is to burn an application program containing plug-ins for a user terminal again, or just replace the plug-ins required to be updated. This method needs to face the user directly, so it can not be done automatically. If there are a large number of users, the workload will be great, which results in greatly increased costs. Therefore it is disadvantageous for the maintenance of the CA system. Especially in the CMMB system, due to the use of the broadcast mode, the terminal and the front end can not have a two-way interaction, thus limiting the security of the system to a large extent. Moreover, if the CA plug-in is not updated regularly, the security of the system may not be guaranteed. Consequently, for the security, scalability, and convenience of the system, the mobile multimedia broadcast is required to provide a device and method for updating a CA plug-in automatically.